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Taking A Closer Look At Transmissions of Big Rig Trucks

A decade ago, transmission controls where found in the traditional spot: Between the cab seats. Today, that paradigm has changed, with dash- and column-mounted controls increasingly taking center stage. This evolution leaves transportation companies in a bind where spec’ing transmissions is concerned.

The fact is, if you have been relying on the same manual transmission since the start of your transportation company, it may be time to give newer options a second look. Modern, advanced transmissions offer a variety of advanced features designed to increase safety, improve performance, and allow for greater efficiency.

Whether it be through predictive cruise control or predictive shifting, new powertrain technologies allow truck drivers to operate their vehicles in a far more seamless and effective fashion. Look-ahead technologies provide for better shifting decisions and increased fuel economy and truck driver comfort. Not only are these factors better for the bottom line, they also help improve truck driver recruiting and retention. Automation isn’t a bad word when it comes to your powertrain.

Fleet managers no longer have room to ignore these options now that they are more plentiful and have come down in cost. There are big benefits to ensuring the right transmission is spec’d for the job. Today, we will look at everything from fuel savings to reduced maintenance and decreased truck driver fatigue. Let’s dig a little deeper.

Drive Specs

The first aspect we will look at is whether you should invest in direct or overdrive transmission layouts. What it really comes down to is the following:

  • Application
  • Route
  • Payload
  • Vehicle speed

There are differenced between direct drive and overdrive efficiency when in gear. Truck drivers typically prefer direct drive at lower speeds when running with lighter loads over even terrain. Direct drive efficiency stems from the fact that its top gear is one, which is one of the most efficient ways a transmission can operate. Since there is less loss, fuel efficiency is a bit higher in this configuration.

Still, as gear efficiency has improved with newer overdrive models, the difference in fuel efficiency between direct and overdrive transmissions. This is born out in the fact that many fleets are now opting for overdrive over direct drive models. No matter what duty cycle a fleet is running, advanced overdrive transmissions now provide a balanced level of increased performance and better fuel economy. If a rig is running a 52,000-pound rear axle, overdrive transmissions provide a wider range of ratios.

This does not mean that there are no scenarios where direct drive is a better option, however. For a truck running at 65 mph or less, direct drivelines provide greater efficiency. At higher speeds, overdrive provides an advantage. Rear axle configurations are also catching up with direct drive variants. OEMs are releasing mid-to-lower ratio transmissions. These ratios allow operators to work with direct drive transmissions at much higher road speeds without sacrificing engine performance.

Manual/AMT/Automatic Specs

When it comes to shifting, fleets have three variants they can work with:

  • Manual
  • Automated manual (AMT)
  • Automatic

Manual transmissions have been around practically since the dawn of time. Fleets who prefer manual variants do so because they are familiar, simple, reliable and inexpensive. Yet, the new problem with manual transmissions can be traced to the ongoing truck driver shortage. Newer, less-experienced truck drivers have a higher learning curve when operating with manual transmissions, which has caused fleets to increasingly switch to AMTs.

To make matters even more interesting, the line has been blurring between what people consider “automated” and “automatic.” Some OEMs, such as Paccar, are going with the term automated since that is how they are designing them. The big benefits of these transmissions, whatever you call them, are plentiful.

New truck drivers catch on quickly when they are operating a big rig that operates like a traditional automatic transmission passenger car. When they can just put in gear and go, they are less likely to fumble around or make a mistake in a hazardous situation; their eyes stay on the road, distractions are reduced, and thy suffer less fatigue related to operating a manual transmission.

Automated and automatic transmission varieties also save fleets big bucks over the long term. When fleet managers can rely on solid performance, increase fuel savings, decrease maintenance, and improve truck driver skills levels, the bottom line gets a little fatter.

Safety gains are accomplished when truck drivers do not have to spend a moment considering whether they should shift when running on a grade. This makes them great candidates if a route is running through hill country. Down shifting decisions are made by the vehicle and not by the truck driver. For downspeeding, engine speeds are too low for manual transmissions to be effective. Either the truck driver is shifting too much, too little, or not fast enough.

In downspeeding applications, the fuel savings come in around 10% above what a truck driver may see downshifting with an AMT or a manual transmission. If there is one downside to automated or automatic transmissions for big rigs, it is the price point. Some motor carriers may not be in a position to make the required investment in these technologies.

Generally, when a fleet specs a manual transmission, they will do so either because they want to save money, operate with an experienced truck driver pool, or are running freight in a specific and sometimes challenging application, such as a wrecker service. Sometimes the truck driver must always be in full control.

Specific applications requiring manual transmissions are shrinking, however. Whether you are talking about a split box transmission on a vacuum truck or otherwise, AMTs are coming out that can handle such situations. Currently, the only application where a manual is a necessary requirement is in the heavy haul sector. The question now is: How long before that changes?

Shifter Specs

Let’s get back to those newfangled shifting options we discussed earlier. While there may be three varieties of transmission specs, there are now four different varieties of shifter specs:

  • Between the seat
  • Dash-mounted
  • Push-button
  • Column-mounted

Some OEMs are pushing shifters into the steering column and incorporating break controls into them as well, which provides a sort of one-stop-shop vehicle control situation for the truck driver. In this configuration, truck drivers no longer have to isolate the separate gear, brake controller and brake actuator all while piloting the vehicle.

Manufacturers call this layout intuitive because it provides easy access to the engine break, shifting, and various transmission states. Drivers do not need to take their eyes off the road and their comfort and distraction level is improved.

Other applications call for dash shifters, mainly because there are already so many controls built into the steering column. This allows the transmission to operate independently without truck drivers having to make decisions they may not be familiar with if they are not experienced enough. Having a shifter in the dash board keeps it within reach but allows for it to also be separated from other controls.

Telematics Specs

With vehicle telematics and connectivity increasingly becoming mandatory options for motor carriers, it was only a matter of time before the powertrain systems were incorporated into the picture. Telematics allow for real-time monitoring of vehicle components, action plans for fault codes, and customized reporting.

Going with our previous OEM example, Paccar has now made remote diagnostics capabilities standard on all its components. Other manufacturers have put transmission monitoring on the plate. Allison offers telematic capabilities that allow for the monitoring of over 170 transmission conditions. When you have this kind of plentiful and real-time data at your fingertips, lots of good things happen.

Many are now viewing telematics as a way to get far more insight into how a truck is doing. Advanced sensor technology can continually monitor how a transmission is performing and report back to the home office instantly. Trouble codes and alerts provide greater insight than ever before, and now that these technologies are being built directly into transmissions, not spec’ing a transmission that utilizes them becomes a missed opportunity.

Remanufacured Specs

Finally, we want to address remanufactured transmissions. While these may not be for everyone, they offer a great way for cash-strapped fleets to save money in a pinch. A remanufactured transmission should generally last one more lifecycle of a rig.

When a fleet chooses a company that completely disassembles, cleans, and inspects remanufactured transmissions, they can generally count on a quality product for a fraction of the price. Wear items should have been replaced and the transmission reassembled with new tooling and gauging. Once the transmission is put together, it should be thoroughly tested to make sure it performs how it should. The last thing a company wants is to sell motor carriers on faulty products.

Still, fleets should take great care on whether they want to go with a remanufactured product. It is important that what they use meets OEM specs, outlines warranty information, and provides nationwide coverage and labor cost exemptions.

We now live in a time where there are far more options than the standard, manual transmission. While this application is great for some fleets, it is critical that fleet managers do their homework on which transmission is best for their application. In this scenario, everyone wins.

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